1. Field of the Invention
This invention relates to devices used in diagnosing dental disorders and more particularly to a temporomandibular joint (TMJ) disorder diagnosis device which can be incorporated into a dental instrument handle, especially the handle of a dental mirror.
2. Description of the Related Art
The temporomandibular joint is the joint which allows articulation of the lower jawbone and is generally present forwardly adjacent the human ear. When the temporomandibular joint articulates normally, the mouth opens and closes per its normal operation without pain, restriction or hyperextension. Similarly, the jaw may be laterally articulated to the left and right, helping the teeth to grind food between them while chewing.
Normally, the vertical articulation of the jaw with the skull ranges from approximately forty millimeters (40 mm) to sixty millimeters (60 mm) from tooth top to tooth top across the open mouth, with vertical articulation of forty-five millimeters (45 mm) being normal. Laterally, the temporomandibular joint allows an articulation of approximately seven millimeters (7 mm) from side to side. Measurement of these articulation distances serves to indicate proper functioning of the temporomandibular joint.
Diseases or disorders of the temporomandibular joint (TMDs) are very common, but frequently overlooked. Such disorders can cause the patient grave discomfort and can be confused with other medical problems so as to obscure an initial correct diagnosis. TMDs affect proper jaw articulation and can have an overall effect upon the general well being of the person suffering such disorder. Generally, deviations from normal articulation indicates a problem with one or both of the temporomandibular joints. Generally, if the patient's mouth can only open twenty-five millimeters (25 mm) or less, or if pain is present, further evaluation needs to take place in order to determine the presence of a TMD. Similarly, if as the patient slowly opens the mouth, the jaw deviates from a straight line departure from the skull, a TMD is indicated. Hyperextension of the temporomandibular joint is indicated when the patient is able to open the mouth sixty millimeters (60 mm) or more. Should the lateral articulation of the jaw significantly exceed seven millimeters (7 mm) or if the lateral articulation is restricted, there may also be a problem with the TMJ that requires further evaluation.
Diagnosis or determination of initial TMJ problems are fairly straightforward as it is the articulation distances that need to be determined for the open mouth and its side to side articulation. Furthermore, the jaw should open from the skull in a straight line manner, and not deviate from that straight line at an angle or in a sinuous motion. While a simple ruler would provide the required measurements, such rulers are not specifically marked for TMDs and are not readily at hand for most dentists or dental assistants. Furthermore, the specific distances for TMDs may not be easily recalled or may be mistakenly recalled during the diagnosis. Such pertinent diagnostic information is as a small drop in the ocean of knowledge a dentist must embody in order to serve the patient well. For these reasons, even though it is relatively easy to measure the critical TMJ distances, such measurements are sometimes neglected. In 1989, the failure to diagnose dental injuries accounted for approximately one third of legal claims while TMJ problems accounted for approximately five (5) to ten (10) percent of such claims.
While dental practitioners (including dentists and dental assistants) are one group that use TMJ measurements in order to assess injury or disease, emergency room physicians also require means by which TMJ articulation can be determined in order to evaluate any problems that may be present with the joint. Similarly, plastic surgeons and head-and-neck surgeons sometimes require the patient's mouth to be held open by artificial means during surgery and the mouth opening should be determined accurately. All other health care practitioners seeking or requiring measurement of the TMJ articulation likewise require tools by which such measurement may be made.